1. Field of the Invention
The present invention relates to sheet feed devices and image forming apparatuses, and more particularly to detection of a state of a paper stack cassette in a sheet feed device.
2. Description of the Related Art
An image forming apparatus is connected to various optional units, such as a sheet feed device, to extend functions thereof. The image forming apparatus needs to confirm a state of the sheet feed device to perform a feed operation or a conveyance operation, and one type of such confirmation is confirmation of an open/closed state of a paper stack cassette. Also, detection of the open/closed state of the paper stack cassette can be used in transition from a sleep state to a standby state, and it is therefore also sought from the viewpoint of usability that the open/closed state of the paper stack cassette is detected during an energy saving mode.
In a conventional connection between an image forming apparatus and a sheet feed device, a controller of the image forming apparatus can be connected to a controller of the sheet feed device via a communication line. The image forming apparatus transmits and receives information regarding the sheet feed device through the communication line, and this information includes information regarding the open/closed state of a paper stack cassette, and the like (see Japanese Patent Laid-Open No. 2008-080799). Also, for detection of the open/closed state of the paper stack cassette, a configuration is available in which detection of the paper size of recording materials contained in the paper stack cassette and detection of the open/closed state of the paper stack cassette are recognized based on the on/off combination of a plurality of detection switches. This is an inexpensive configuration in which the number of the detection switches is reduced, compared with a configuration in which a switch dedicated to the open/closed state of the paper stack cassette is provided (e.g., see Japanese Patent Laid-Open No. 2003-081446).
FIG. 10 shows a diagram of control system blocks for detecting an open/closed state of the paper stack cassettes by a conventional method. An image forming apparatus 100 includes a first detection unit 200, and sheet feed devices 150a and 150b include second detection units 250a and 250b, respectively, that are operated with a power source dedicated to the sheet feed devices. The first detection unit 200 and the second detection units 250a and 250b are connected to each other via a communication line 210. In the sheet feed device 150a, a detection switch unit 252a is connected to the second detection unit 250a. Similarly, in the sheet feed device 150b, detection switch units 252b and 252c are connected to the second detection unit 250b. As an example of control, a controller of the image forming apparatus 100 is used for the first detection unit 200, and controllers of the sheet feed devices are used for the second detection units 250a and 250b. As the detection switch units 252a, 252b, and 252c, a plurality of switches that are turned on/off in conjunction with the paper stack cassettes are used. The controllers of the sheet feed devices detect the paper size and the open/closed state of the paper stack cassettes, and the information is conveyed to the controller of the image forming apparatus via the communication line 210.
However, to detect the open/closed states of the paper stack cassettes by the aforementioned conventional method, the controllers that serve as the second detection units of the sheet feed devices need to be operated. Therefore, the controllers of the sheet feed devices cannot be turned off even during the energy saving mode, and a problem arises in that power consumption for the controllers of the sheet feed devices increases.
On the other hand, to detect the open/closed states of the paper stack cassettes without operating the controllers of the sheet feed devices during the energy saving mode, a configuration shown in FIG. 11, for example, needs to be employed. In FIG. 11, in addition to the configuration of FIG. 10, the detection switch units 252a, 252b, and 252c are directly connected to the first detection unit 200 of the image forming apparatus 100 through signal lines. During the energy saving mode, it is possible to notify the first detection unit 200 of information regarding the detection switch units 252a, 252b, and 252c with these signal lines, rather than via the second detection units and the communication line 210. FIG. 11 shows the case where each detection switch unit has two switches, and in this case, the number of signal lines increases by six. However, the number of switches may be selected as appropriate in accordance with paper type, model, or the like, and in that case, the number of signal lines increases by the number obtained by multiplying the number of detection switches by the number of the sheet feed devices. Consequently, a problem arises in that costs rise due to an increase in signal lines or the like to detect the open/closed states of the paper stack cassettes by suppressing the above-mentioned increase in power consumption during the energy saving mode.